1. Field of the Invention
The present invention relates to a fuel cartridge for a fuel cell and a fuel cell with the fuel cartridge.
2. Description of the Related Art
With the advent of recent information society, the amount of information processed in an electronic device, e.g., a personal computer, dramatically increases, and power consumption in the electronic device has remarkably increased due to the increase of the amount of information. Particularly, in a portable electronic device, the increase in power consumption because of the increase in processing capacity presents a problem. Currently, in such a portable electronic device, a lithium-ion battery is generally used as a power source, and the energy density of the lithium-ion battery has been close to the theoretical limit. Therefore, there is a constraint that the drive frequency of CPU (central processing unit) must be controlled to reduce the power consumption in order to extend the continuous use period of the portable electronic device.
Under these circumstances, a fuel cell with a high energy density and a high heat exchange rate is used as a power source instead of the lithium-ion battery with the expectation that the continuous use period of the portable electronic device will be improved substantially.
The fuel cell is composed of a fuel pole, an oxidizer pole (hereinafter, these are also called “catalyst electrodes”), and an electrolyte between these poles. Fuel is supplied to the fuel pole and an oxidizer is supplied to the oxidizer pole to generate electric power by an electrochemical reaction. Hydrogen is generally used as the fuel. However, recently, by using methanol that is inexpensive and is handled easily as a raw material, a methanol reforming type fuel cell, in which methanol is reformed to generate hydrogen, and a direct type fuel cell, in which methanol is directly used as fuel, are being actively developed.
When hydrogen is used as the fuel, the reaction at the fuel pole is represented by the following equation (1).3H2→6H++6e−  (1)
When methanol is used as the fuel, the reaction at the fuel pole is represented by the following equation (2).CH3OH+H2O→6H++CO2+6e31   (2)
Also, in both cases, the reaction at the oxidizer pole is represented by the following equation (3).3/2O2+6H++6e−→3H2O  (3)
Particularly, in the direct type fuel cell, since hydrogen ions can be obtained from a methanol aqueous solution, no device for reforming or the like is required, and there is a big advantage in applying this to a portable electronic device. Further, since a liquid methanol aqueous solution is used as the fuel, direct type fuel cell has an advantage that the energy density is exceedingly high.
In such a liquid fuel supply type fuel cell, preferably, concentration of the fuel component is high in the liquid to be supplied to the fuel pole, in terms of putting the fuel cell to use for an extended period.
However, when organic liquid fuel, such as methanol, that has a high affinity for water is used, according as the concentration of the fuel component becomes higher, a crossover in which the fuel component is diffused in a solid electrolyte film including water to reach the oxidizer pole is more apt to occur. The crossover causes lowering in voltage and output and reduction in fuel efficiency, because the organic liquid fuel that should provide electrons at the fuel pole is oxidized at the oxidizer pole side and is not used effectively as the fuel. Therefore, it is difficult to increase the concentration of fuel component in the liquid to be supplied to the fuel pole.
So, there is proposed a fuel cell including a fuel tank which contains high-concentration methanol and a mixing tank used to dilute the methanol in the fuel tank with water (Japanese Patent Laid-open No. 2003-223243). This conventional art adopts an arrangement in which water generated by the reaction of the above-mentioned equation (3) is introduced to the mixing tank in order to dilute the high-concentration methanol and then diluted methanol is supplied to the fuel cell, in a fuel cell used in a notebook type personal computer.
However, this arrangement has room for improvement in regard to stable supply of liquid fuel at a predetermined concentration of fuel component to the fuel cell. Also, since a mechanism for introducing water generated at the oxidizer pole into the mixing tank is required, the device arrangement is complex.